The interaction between the pituitary hormone, adrenocorticotropin (ACTH), and melanocortin-2 rec... more The interaction between the pituitary hormone, adrenocorticotropin (ACTH), and melanocortin-2 receptor (MC2R) orthologs involves the H6 F7 R8 W9 and R/K15 K16 R17 R18 motifs in ACTH making contact with corresponding contact sites on MC2R. Earlier studies have localized the common HFRW binding site of all melanocortin receptors to residues in TM2, TM3, and TM6 that are located close to the extracellular space. The current study has identified residues in Xenopus tropicalis (xt) MC2R in TM4 (I158, F161), in EC2 (M166), and in TM5 (V172) that also are involved in activation of xtMC2R, and may be in the R/KKRR contact site of xtMC2R. These results are compared to earlier studies on the corresponding domains of human MC2R and rainbow trout MC2R in an effort to identify common features in the activation of teleost and tetrapod MC2R orthologs following stimulation with ACTH.
The evolution of the melanocortin receptors (MCRs) is closely associated with the evolution of th... more The evolution of the melanocortin receptors (MCRs) is closely associated with the evolution of the melanocortin-2 receptor accessory proteins (MRAPs). Recent annotation of the elephant shark genome project revealed the sequence of a putative MRAP1 ortholog. The presence of this sequence in the genome of a cartilaginous fish raises the possibility that the mrap1 and mrap2 genes in the genomes of gnathostome vertebrates were the result of the chordate 2R genome duplication event. The presence of a putative MRAP1 ortholog in a cartilaginous fish genome is perplexing. Recent studies on melanocortin-2 receptor (MC2R) in the genomes of the elephant shark and the Japanese stingray indicate that these MC2R orthologs can be functionally expressed in CHO cells without co-expression of an exogenous mrap1 cDNA. The novel ligand selectivity of these cartilaginous fish MC2R orthologs is discussed. Finally, the origin of the mc2r and mc5r genes is reevaluated. The distinctive primary sequence cons...
General and Comparative Endocrinology, Aug 1, 2007
In gnathostomes there is remarkable consistency in the organization of the proenkephalin gene. Th... more In gnathostomes there is remarkable consistency in the organization of the proenkephalin gene. This opioid precursor encodes seven opioid (YGGF) sequences: five pentapeptide sequences, a met-enkephalin-7 sequence and a met-enkephalin-8 sequence. Yet, within vertebrate lineages there can be distinct sets of pentapeptide opioids (YGGFM or YGGFL). In the Sarcopterygii, the sixth opioid position in lungfishes and anuran amphibian proenkephalin genes encodes a met-enkephalin (YGGFM) sequence. However, in mammalian proenkephalin there is a leu-enkephalin (YGGFL) sequence at this position. This study was done to test the hypothesis that the presence of the leu-enkephalin sequence in mammals is a feature common to amniote vertebrates, but not present in anamniote vertebrates. To resolve this issue, proenkephalin cDNAs were cloned from the urodele amphibians, Amphiuma means and Necturus maculosus, and two amniote vertebrates, the turtle, Chrysemys scripta, and the brown snake, Storeria dekayi. As predicted, a met-enkephalin sequence is present at the sixth opioid position in urodele amphibians; whereas, a leu-enkephalin sequence is present at this opioid site in the reptile proenkephalin sequences. These data are consistent with the conclusion that the transition from a met-enkephalin sequence to a leu-enkephalin sequence at the sixth opioid position in tetrapod proenkephalins occurred in the ancestral proto-reptiles. Phylogenetic analyses, using the Maximum Parsimony and Neighbor-Joining algorithms, of the amphibian proenkephalin sequences supported the position that anuran and urodele amphibians are a monophyletic assemblage. The same analysis of reptile-related proenkephalin sequences, including the deduced amino acid sequence of a partially characterized alligator proenkephalin cDNA, could not conclusively resolve the phylogeny of the major reptilian orders.
General and Comparative Endocrinology, Sep 30, 2007
In many cartilaginous fishes, most ray-finned fishes, lungfishes, and amphibians, the post-transl... more In many cartilaginous fishes, most ray-finned fishes, lungfishes, and amphibians, the post-translational processing of POMC includes the monobasic cleavage of β-endorphin to yield an opioid that is eight to ten amino acids in length. The amino acid motif within the β-endorphin sequence required for a monobasic cleavage event is -E-R-(S/G)-Q-. Mammals and birds lack this motif and as a result
General and Comparative Endocrinology, Jul 31, 2003
A distinctive feature of the pituitary hormone precursor, proopiomelanocortin (POMC), is the pres... more A distinctive feature of the pituitary hormone precursor, proopiomelanocortin (POMC), is the presence of multiple melanocortin core sequences (HFRW), and one copy of the opioid, beta-endorphin. In the older lineages of ray-finned fish (i.e., orders Acipenseriformes and Semionotiformes), certain extant lobe-finned fish (Australian lungfish and African lungfish), and the tetrapods there are three melanocortin regions in POMC: ACTH/alphaMSH, beta-MSH, and gamma-MSH. However, among the teleosts, the most recent radiation of the ray-finned fishes, the gamma-MSH sequence is absent from the POMC genes of euteleosts like the carp, tilapia, chum salmon, sockeye salmon, and rainbow trout. The objective of this study was to determine whether the gamma-MSH sequence still may be present in the POMC gene of a more basal lineage of the teleosts such as a representative from subdivision Elopomorpha. To this end, a POMC cDNA was cloned and sequenced from the pituitary of the American eel, Anguilla rostrata (order Anguilliformes, family Anguillidae). The open reading frame of the eel POMC cDNA was 648 nucleotides in length and encoded 216 amino acids. As predicted, eel POMC contained the deduced amino acid sequences for beta-endorphin, ACTH/alpha-MSH, and beta-MSH. These end-products displayed primary sequence features that are common to ray-finned fish. Eel POMC lacks a gamma-MSH sequence and a large portion of the joining peptide region. In this regard, the eel POMC gene thus displays features very similar to the POMC genes that have been sequenced from euteleosts. Although it is conceivable that the gamma-MSH sequence may be present in representatives from the other basal extant lineages of teleosts (i.e., subdivisions Osteoglossomorpha or Clupeomorpha), it is also possible that the deletion that resulted in the loss of the gamma-MSH sequence occurred in the ancestral neopterygian that gave rise to the teleosts. In this case, the gamma-MSH sequence should be absent in all extant teleosts.
The interaction between the pituitary hormone, adrenocorticotropin (ACTH), and melanocortin-2 rec... more The interaction between the pituitary hormone, adrenocorticotropin (ACTH), and melanocortin-2 receptor (MC2R) orthologs involves the H6 F7 R8 W9 and R/K15 K16 R17 R18 motifs in ACTH making contact with corresponding contact sites on MC2R. Earlier studies have localized the common HFRW binding site of all melanocortin receptors to residues in TM2, TM3, and TM6 that are located close to the extracellular space. The current study has identified residues in Xenopus tropicalis (xt) MC2R in TM4 (I158, F161), in EC2 (M166), and in TM5 (V172) that also are involved in activation of xtMC2R, and may be in the R/KKRR contact site of xtMC2R. These results are compared to earlier studies on the corresponding domains of human MC2R and rainbow trout MC2R in an effort to identify common features in the activation of teleost and tetrapod MC2R orthologs following stimulation with ACTH.
The evolution of the melanocortin receptors (MCRs) is closely associated with the evolution of th... more The evolution of the melanocortin receptors (MCRs) is closely associated with the evolution of the melanocortin-2 receptor accessory proteins (MRAPs). Recent annotation of the elephant shark genome project revealed the sequence of a putative MRAP1 ortholog. The presence of this sequence in the genome of a cartilaginous fish raises the possibility that the mrap1 and mrap2 genes in the genomes of gnathostome vertebrates were the result of the chordate 2R genome duplication event. The presence of a putative MRAP1 ortholog in a cartilaginous fish genome is perplexing. Recent studies on melanocortin-2 receptor (MC2R) in the genomes of the elephant shark and the Japanese stingray indicate that these MC2R orthologs can be functionally expressed in CHO cells without co-expression of an exogenous mrap1 cDNA. The novel ligand selectivity of these cartilaginous fish MC2R orthologs is discussed. Finally, the origin of the mc2r and mc5r genes is reevaluated. The distinctive primary sequence cons...
General and Comparative Endocrinology, Aug 1, 2007
In gnathostomes there is remarkable consistency in the organization of the proenkephalin gene. Th... more In gnathostomes there is remarkable consistency in the organization of the proenkephalin gene. This opioid precursor encodes seven opioid (YGGF) sequences: five pentapeptide sequences, a met-enkephalin-7 sequence and a met-enkephalin-8 sequence. Yet, within vertebrate lineages there can be distinct sets of pentapeptide opioids (YGGFM or YGGFL). In the Sarcopterygii, the sixth opioid position in lungfishes and anuran amphibian proenkephalin genes encodes a met-enkephalin (YGGFM) sequence. However, in mammalian proenkephalin there is a leu-enkephalin (YGGFL) sequence at this position. This study was done to test the hypothesis that the presence of the leu-enkephalin sequence in mammals is a feature common to amniote vertebrates, but not present in anamniote vertebrates. To resolve this issue, proenkephalin cDNAs were cloned from the urodele amphibians, Amphiuma means and Necturus maculosus, and two amniote vertebrates, the turtle, Chrysemys scripta, and the brown snake, Storeria dekayi. As predicted, a met-enkephalin sequence is present at the sixth opioid position in urodele amphibians; whereas, a leu-enkephalin sequence is present at this opioid site in the reptile proenkephalin sequences. These data are consistent with the conclusion that the transition from a met-enkephalin sequence to a leu-enkephalin sequence at the sixth opioid position in tetrapod proenkephalins occurred in the ancestral proto-reptiles. Phylogenetic analyses, using the Maximum Parsimony and Neighbor-Joining algorithms, of the amphibian proenkephalin sequences supported the position that anuran and urodele amphibians are a monophyletic assemblage. The same analysis of reptile-related proenkephalin sequences, including the deduced amino acid sequence of a partially characterized alligator proenkephalin cDNA, could not conclusively resolve the phylogeny of the major reptilian orders.
General and Comparative Endocrinology, Sep 30, 2007
In many cartilaginous fishes, most ray-finned fishes, lungfishes, and amphibians, the post-transl... more In many cartilaginous fishes, most ray-finned fishes, lungfishes, and amphibians, the post-translational processing of POMC includes the monobasic cleavage of β-endorphin to yield an opioid that is eight to ten amino acids in length. The amino acid motif within the β-endorphin sequence required for a monobasic cleavage event is -E-R-(S/G)-Q-. Mammals and birds lack this motif and as a result
General and Comparative Endocrinology, Jul 31, 2003
A distinctive feature of the pituitary hormone precursor, proopiomelanocortin (POMC), is the pres... more A distinctive feature of the pituitary hormone precursor, proopiomelanocortin (POMC), is the presence of multiple melanocortin core sequences (HFRW), and one copy of the opioid, beta-endorphin. In the older lineages of ray-finned fish (i.e., orders Acipenseriformes and Semionotiformes), certain extant lobe-finned fish (Australian lungfish and African lungfish), and the tetrapods there are three melanocortin regions in POMC: ACTH/alphaMSH, beta-MSH, and gamma-MSH. However, among the teleosts, the most recent radiation of the ray-finned fishes, the gamma-MSH sequence is absent from the POMC genes of euteleosts like the carp, tilapia, chum salmon, sockeye salmon, and rainbow trout. The objective of this study was to determine whether the gamma-MSH sequence still may be present in the POMC gene of a more basal lineage of the teleosts such as a representative from subdivision Elopomorpha. To this end, a POMC cDNA was cloned and sequenced from the pituitary of the American eel, Anguilla rostrata (order Anguilliformes, family Anguillidae). The open reading frame of the eel POMC cDNA was 648 nucleotides in length and encoded 216 amino acids. As predicted, eel POMC contained the deduced amino acid sequences for beta-endorphin, ACTH/alpha-MSH, and beta-MSH. These end-products displayed primary sequence features that are common to ray-finned fish. Eel POMC lacks a gamma-MSH sequence and a large portion of the joining peptide region. In this regard, the eel POMC gene thus displays features very similar to the POMC genes that have been sequenced from euteleosts. Although it is conceivable that the gamma-MSH sequence may be present in representatives from the other basal extant lineages of teleosts (i.e., subdivisions Osteoglossomorpha or Clupeomorpha), it is also possible that the deletion that resulted in the loss of the gamma-MSH sequence occurred in the ancestral neopterygian that gave rise to the teleosts. In this case, the gamma-MSH sequence should be absent in all extant teleosts.
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